Increasing the connection between treatment research and treatment as it is practiced in community settings (i.e., ecological validity) is essential for translating recent empirically supported approaches to individuals who would benefit most from them. A recent series of federally supported initiatives has focused on enhancing ecological validity by (a) translating findings from federally funded efficacy trials to treatment effectiveness work in real-world settings (particularly with the genesis of the National Drug Abuse Clinical Trials Network) and (b) advancing quantitative methods specifically geared toward addressing the complexities that arise in (and have stifled) treatment research in real-world contexts. The investigation proposed in this R01 application combines work from an ongoing Clinical Trials Network (CTN) effectiveness trial on the most widely used treatment for comorbid substance abuse and PTSD available for women, Seeking Safety, with continuing development, refinement and extension of statistical approaches to handle data from therapy groups when therapy group membership itself changes over time by design. Although progress has been made in developing methods to handle longitudinal data from open-enrollment (also known as "rolling") therapy groups, the most common milieu for treatment delivery in community-based substance abuse programs, several salient critical issues to the stakeholders in substance abuse treatment research remain unresolved and are of primary methodological interest in this investigation. This includes modeling the impact of group membership turnover on (a) the long-term recovery management process, (b) the identification of the active components in ecologically valid treatment trials, and (c) (sub) optimal patient mix in treatment groups and measurement of treatment group (in) stability. The ultimate goal of the proposed secondary data analytic investigation is to place more powerful analytic and methodological tools in the hands of substance abuse and alcoholism treatment researchers for (a) analyzing existing data from open- enrollment groups in a more defensible manner, maximizing the likelihood that incorrect inferences are avoided (i.e., advocating for a treatment that may be ineffective in reality) and that the full complexities of open-enrollment group trials are captured analytically, and/or (b) submitting new applications for trials in all areas of behavioral treatment research with protocols that more closely resemble treatment in community settings. In addition to the practical benefits of the methodological development in this project (e.g., more accurate inferences concerning treatment efficacy, better reflection of the open-enrollment process in data analytic models), this application represents an opportunity for further dissemination, and a more nuanced examination of, what is to date, the largest randomized clinical trial for Seeking Safety. The proposed project seeks to develop more accurate methods to analyze data from open-enrollment substance abuse treatment trials, which present special analytic challenges (i.e., changes in group membership over time). If we are successful in continuing the development and refinement of new modeling tools to address analytic complexities in open-enrollment trials, substance abuse treatment researchers will be positioned to develop federally funded open-enrollment treatment trials that better resemble treatment as it is practiced in community settings. These developments may also facilitate building a "community-friendly" treatment research portfolio for funding agencies that supports substance abuse and alcoholism treatment research.